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Closed or open loop ?

shmbry

New Member
Joined
Nov 24, 2023
Messages
1
Location
uk
Can anyone tell me if this an open or closed loop system. Many thanks.

Hydraulic Schematic-2.png
 

Mobiltech

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Joined
Jan 14, 2014
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1,659
Location
Sask.
Occupation
Self employed Heavy duty mechanic
Open loop. Variable displacement.
 

Mobiltech

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Jan 14, 2014
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1,659
Location
Sask.
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Self employed Heavy duty mechanic
Sorry. I see your right. I saw the electric motor and thought it was controlling output.
 

funwithfuel

Senior Member
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Mar 7, 2017
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5,456
Location
Will county Illinois
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Mechanic
I see a single direction DC motor, shaft driving the fixed displacement motor. I see the DC motor depending on a demand of a function to energize the motor solenoid. In fact it looks very similar to a liftgate power pack running a small backhoe.
 

funwithfuel

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Mar 7, 2017
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Will county Illinois
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Mechanic
a little rusty on the hydraulic 101 stuff. Your saying it’s open loop because of the return off the 160 bar relief?
Yes, all the pump oil hits the pressure reducing valve but runs past it to the return channel. When a function is used, it closes the return passage and performs work up to the value set by the reducing valve, in this case 150 bar. Then the reducing valve opens dumping back to tank.
 

terex herder

Senior Member
Joined
Nov 10, 2017
Messages
1,735
Location
Kansas
The pump gets all its oil from the tank, and all oil is returned to the tank. Open system. A closed loop system will have oil being returned to the pump with a bleed off oil being returned to the tank via a filter, and a charge pump to make up for the lost oil.

Closed loop works great for constant volume systems, such as running motors, hydrostatic drive systems. Not so good for systems that change volume, such as cylinders. When both situations are needed, there is usually a open loop gear pump on the back of the closed loop piston pump.
 
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